1. Field of the Invention
The present invention relates generally to electron beam apparatus and methods of using electron beam apparatus.
2. Description of the Background Art
Apertures to limit the beam current are needed in electron-beam columns to achieve desired beam spot sizes under various column conditions. For example, for a given column condition, a particular current limiting aperture size will be needed to achieve a certain spot size.
Historically, individual current-limiting apertures of various sizes and shapes have been installed on an aperture rod. A mechanism located on the atmospheric side of the electron column (i.e. outside of the high vacuum environment) is used to drive the desired fixed aperture to the optical axis of the column so that it limits the electron beam current.